In a typical FWS filter, when used under suction, the FWS cannot be drained of its water during operation. The vacuum that is created within the filter housing draws air through the drain valve, prohibiting the water from flowing out of the water sump of the FWS. To drain the water, current practices require shutting the engine down or diverting the fuel flow via manual valves to permit draining of the water.
A FWS filter that allows water to be drained from the water sump without shutting the engine down or diverting fuel flow (i.e. without shutting off fuel flow to the FWS filter) is desirable.